1. Field of the Invention
The present invention relates to a plasma display panel. More particularly, the present invention relates to a barrier rib structure of a plasma display panel constructed to prevent colors of phosphor screens from being mixed, and a lower plate structure of the panel using the same.
2. Description of the Related Art
A general discharge display panel is a plasma display panel. The plasma display panel is a flat panel display in which scan and address electrodes are formed in a matrix shape between upper and lower plates to drive pixels, and an image is created using ultraviolet rays generated while generating electric discharge between the electrodes.
FIG. 1 shows the structure of a surface discharge type plasma display panel according to a related art. Referring to FIG. 1, an upper substrate of the plasma display panel includes a pair of bus electrodes 22 and 23 having certain width and height and formed on one side of a front glass substrate 21, a dielectric layer 24 for protecting the bus electrodes 22 and 23 and maintaining electric charges excited during a discharge to discharge the bus electrodes 22 and 23 with a low voltage during a sustain period, and a protection layer 25 on the dielectric layer 24 for preventing the bus electrodes 22 and 23 from being damaged due to strong discharge and for emitting secondary electrons.
Further, a lower substrate of the plasma display panel includes address electrodes 27 formed on one side of a rear glass substrate 26 to selectively select each unit cell and induce an initial discharge. A dielectric layer 33 for insulating the address electrodes 27 is formed on the address electrodes 27. An electric discharge space is formed on the dielectric layer 33, and barrier ribs 28 for separating the unit cells and preventing crosstalk between the adjacent cells are formed in the electric discharge space. Phosphor screens 30, 31 and 32 made of red (R), green (G) and blue (B) phosphors, which are excited by ultraviolet rays generated by the discharge operation to emit visible light, are coated on side surfaces of the barrier ribs 28 and an upper surface of the dielectric layer 33. The barrier ribs 28 are formed either in a stripe shape as illustrated in FIG. 2a or in a closed shape as illustrated in FIG. 2b. 
Accordingly, the electric discharge spaces 29 are formed between the lower and upper substrates. Neon gas, xenon gas, helium gas and the like for electric discharge are injected into the electric discharge spaces 29. A lower surface of the upper substrate is brought into a close contact with an upper surface of the lower substrate of the display panel, and a resultant unit cell of the plasma display panel can be formed accordingly.
In the related art plasma display panel configured as discussed above, a surface discharge occurs to display an image on the display panel, as follows. If an initial discharge voltage is applied to the bus electrodes 22 and 23 and the address electrodes 27 such that the potential difference can be generated between these electrodes, an initial discharge is generated in the electric discharge spaces 29 and ultraviolet rays are then generated while the surface discharge is generated between the pair of the bus electrodes 22 and 23. At this time, the phosphors of the surrounding phosphor screens 30, 31 and 32 are excited by means of the ultraviolet rays and colors are simultaneously displayed.
That is, electrons existing in the electric discharge spaces 29 are accelerated by the applied voltage and collide with an inert mixed gas injected into the electric discharge spaces 29 at a pressure of about 400 to 600 torr to generate ultraviolet rays which in turn collide with the phosphor screens 30, 31 and 32 to generate the visible light. Accordingly, it is possible to display a desired image by combining the cells of the electric discharge spaces 29 in which the electric discharge occurs with the cells of the electric discharge spaces 29 in which the electric discharge does not occur.
However, the foregoing plasma display panel has the following limitations and problems.
In order to display an image on the related art plasma display panel, the phosphor screens 30, 31 and 32 respectively having different colors of red, green and blue are injected into the spaces between the adjacent barrier ribs 28. A screen printing process, an inkjet process, or a dispensing process according to a related art is used to inject the phosphor screens 30, 31 and 32 between the adjacent barrier ribs 28. In the dispensing process, the dispensing materials of the phosphor screens are discharged into the spaces between the respective barrier ribs through discharge holes formed on nozzles. At this time, the discharge hole should be formed such that its diameter is smaller than a gap between the adjacent barrier ribs 28. However, the related art dispensing process has a problem of mixed colors since the phosphor screen materials permeate through the neighboring barrier ribs 28. That is, the related art dispensing process for forming the phosphor screens 30, 31 and 32 has the following problems.
In a case where the barrier ribs 28 are formed in a stripe shape as illustrated in FIG. 2a, due to unstable control of the discharge pressure of the phosphor screen materials, an excessive discharge of the phosphor screen materials is partially generated on a portion where the phosphor screen materials start to be coated. Further, the excessive discharge of the phosphor screen materials allows the phosphor screen materials to permeate through the neighboring barrier ribs by means of a capillary phenomenon, because spaces between the discharge holes of the nozzles and the barrier ribs 28 are very small. This creates another problem wherein the colors of the phosphor screens 30, 31 and 32 between the adjacent discharge spaces 29 are mixed. This problem also occurs at a portion where the discharge of the phosphor screens 30, 31 and 3, as well as the portion where the discharge of the phosphor screens is started.
Furthermore, in a case where the barrier ribs 28a and 28b are formed in a closed shape as illustrated in FIG. 2b, the phosphor screens 30, 31 and 32 may be coated even on the lateral barrier ribs 28b when executing the continuous pattern coating. Therefore, there is another problem wherein the phosphor screens coated on the lateral barrier ribs 28b flow into neighboring discharge spaces 29 along the barrier ribs 28b, which results in the undesired mixing of colors of the phosphor screens.